This invention relates generally to a press machine, and more particularly to a press machine having a composite piston assembly, an interchangeable alignment system, a lubricant recovery system, a pressurized fluid control system, and a method for aligning the die assemblies of the press.
Generally, a punch press is designed to form stampings from a strip of steel or other suitable material. A punch press, such as that disclosed in U.S. Pat. No. 3,213,729, issued to Richard C. Koch, typically has two die assemblies. The first die assembly, which includes a button die, a punch, and a knockout, is attached to a piston which reciprocates back and forth within a cylinder. The piston is connected to a crankshaft, which is rotated by a motor. The second die assembly includes a stripper assembly having a compound blank and a stripper insert. The second die assembly is substantially fixed to the frame of the press machine.
In the operation of a conventional press machine, a strip of stock to be stamped is inserted between the first and second die assemblies, the die assemblies having been previously axially aligned with respect to one another. As the motor turns the crankshaft, the piston is advanced towards the strip of stock. This causes the first die assembly to receive the compound blank, thereby piercing and punching the strip of stock in the process. At the same time, the punch of the first die assembly enters the compound blank of the second die assembly to blank and pierce the stamping from the strip of stock. In so doing, the button die pushes the stripper assembly inwardly into the second die assembly, compressing springs which press against the stripper assembly.
As the piston of the press is retracted, the springs force the stripper assembly towards the strip of stock to strip the stock from the compound blank. A slug of the stock material is also cleared from the inside of the compound blank.
As the piston retracts fully, the knockout of the first die assembly engages a stop bar, and in so doing, is advanced to strip away the stamped part from the button die and off of the punch of the first assembly.
A problem with press machines arises in aligning the first and second die assemblies with respect to one another. Axial alignment of the two die assemblies is essential for proper stamping of a part. Generally, alignment adjustments are made with the second die assembly, since the first die assembly is attached to the piston, thereby causing alignment adjustment of the first die assembly to be impractical. An important consideration is the elevation of the second die assembly with respect to the elevation of the first die assembly. In a press machine such as the 11/2 inch diameter, four ton capacity, horizontal press manufactured by Hovis Precision Products, Division of Rochez Bros., Inc., of Simpsonville, S.C., the second die assembly is carried in alignment, or receiver, blocks. The receiver blocks are held in a receptacle in the frame of the press machine.
In order to achieve proper elevational alignment of the second die assembly, the base of the receiver block must be precision-ground, which is a time-consuming and expensive process. After the receiving block has been precision-ground, it may be used good for that particular machine only and generally would not be usable with a subsequent machine. Should the receiving block be ground down too far, the receiving block would not be usable, and the cost for such a receiving block and the machining done on the block to that point would be lost.
Another problem arises in increasing the tonnage capacity of a press. In so doing, the size and mass of the piston for the press must be increased accordingly. However, the manufacture of a piston having the necessary size and mass for use in a press of, for example, a 20 ton capacity, is impractical and unduly expensive.
Turning from alignment of the die assemblies of a press to the ejection of the stamped parts and resulting slugs from the press, U.S. Pat. No. 4,268,780, issued to Charles D. Hicks, discloses an air ejector system for shedding and ejecting a slug from a central punch of a punch machine. The air is controlled by a spring-loaded, cam-actuated, three-way valve which opens or closes the air flow from an air supply line responsive to the position of a moving die assembly. While such an air ejection system is effective, the timing of the air delivery to the die assembly is not readily varied.
Inherent to the operation of many metal-working machines, including press machines, is the fact that lubricating fluid delivered to the machines during their operation tends to leak from those lubricated portions of the machines. Such leaking lubricating fluid tends to collect on the exterior surfaces of the machine, causing dust and dirt to adhere to the lubricant on the machine's surfaces, thereby causing a dirty and grimy coating to form on the machine's surface. Not only is such a coating unsightly, but it could potentially impede the manufacturing cleanliness necessary to produce precision parts. Moreover, the leaking lubricant tends to collect on the shop floor around the machines, thereby potentially interfering with movement about the machine by workers and equipment. Finally, because the leaking fluid is typically not recovered but instead is wasted and not reused, new lubricant must be provided to the machines to replace that which is lost through leakage, thereby requiring further use of our limited natural resources for providing lubricating fluid.
Other patented components for press machines are disclosed in U.S. Pat. No. 2,699,830, issued to Hugh M. Hodge, which discloses readily interchangeable punch and die equipment, and U.S. Pat. No. 4,662,256, issued to Charles D. Hicks, which discloses an improved die set where knockout pins of the die set may be replaced without requiring realignment of the die and die retaining components.